Downloading multiple images takes up a lot of RAM in VR

I present my problem / concern.
I am developing an App in which I have a skybox of 6 sides and this represents a place, then to go forward to the next place I should replace the textures with the following ones ... and so on. So to make it look more fluid, I use another cubemap maintaining the previous texture and through an animation I made a "fade" effect after downloading the new textures, showing the skybox with 6 sides.

Here I call the coroutina that downloads the textures of the 6-sided skybox:

Code (CSharp):

1. StartCoroutine (CorFrame ("_ RightTex", ServerUrl + nx + ext));
2. StartCoroutine (CorFrame ("_ DownTex", ServerUrl + ny + ext));
3. StartCoroutine (CorFrame ("_ BackTex", ServerUrl + nz + ext));
4. StartCoroutine (CorFrame ("_ LeftTex", ServerUrl + px + ext));
5. StartCoroutine (CorFrame ("_ UpTex", ServerUrl + py + ext));
6. StartCoroutine (CorFrame ("_ FrontTex", ServerUrl + pz + ext));
7. StartCoroutine (Wait ());

Texture download method:

Code (CSharp):

1.  private IEnumerator CorFrame(string nameTex, string url)
2. {
3.       Destroy(skybox.GetTexture(nameTex));
4.       UnityWebRequest www =
5.       UnityWebRequestTexture.GetTexture(url);
6.       // Wait for download to complete
7.       yield return www.SendWebRequest();
8.       if (www.isNetworkError)
9.       {
10.           Debug.Log(www.error);
11.       }
12.       else
13.       {
14.           skybox.SetTexture(nameTex,
15.          
16.          Instantiate(DownloadHandlerTexture.GetContent(www)));
17.          skybox.GetTexture(nameTex).wrapMode =
18.          TextureWrapMode.Clamp;
19.           Destroy(DownloadHandlerTexture.GetContent(www));
20.           countFrame++;
21.         }
22. }

Then I wait for it to finish downloading the 6 textures showing the cubemap with the previous textures and at the end I apply the fade effect as follows:

Code (CSharp):

1. private IEnumerator FadeOutAnimation ()
2. {
3.      // Get current color
4.       Color spriteColor =
5.      mngBttnInteraction.cubeMap.GetComponent
6.     <MeshRenderer> (). Material.color;
7.     float counter = 0;
8.     float duration = 0.5f;
9.     float alpha = 1;
10.     while (alpha> 0)
11.     {
12.         counter + = Time.deltaTime;
13.         // Fade from 1 to 0
14.         alpha = Mathf.Lerp (1, 0, counter / duration);
15.         // Change alpha only
16.        SetAlpha (spriteColor, alpha);
17.        yield return null;
18.     }
19.     // Disable cubemap
20.     mngBttnInteraction.cubeMap.SetActive (false);
21.     SetAlpha (spriteColor, 1);
22.     // Destroy textures cubemap
23.     for (int i = 0; i <6; i ++)
24.     {
25.         DestroyImmediate
26.        (mngBttnInteraction.cubeMap.GetComponent
27.       <MeshRenderer> (). Materials [i] .GetTexture ("_ MainTex"),
28.       true);
29.     }
30.     // Update with new textures of skybox
31.     mngBttnInteraction.cubeMap.GetComponent
32.     <MeshRenderer> (). materials [0] .SetTexture ("_ MainTex",
33.     (Texture2D) Instantiate (skybox.GetTexture ("_ DownTex")));
34.     mngBttnInteraction.cubeMap.GetComponent
35.     <MeshRenderer> (). materials [1] .SetTexture ("_ MainTex",
36.     (Texture2D) Instantiate (skybox.GetTexture ("_ UpTex")));
37.     mngBttnInteraction.cubeMap.GetComponent
38.     <MeshRenderer> (). materials [2] .SetTexture ("_ MainTex",
39.     (Texture2D) Instantiate (skybox.GetTexture ("_ RightTex")));
40.     mngBttnInteraction.cubeMap.GetComponent
41.     <MeshRenderer> (). materials [3] .SetTexture ("_ MainTex",
42.     (Texture2D) Instantiate (skybox.GetTexture ("_ FrontTex")));
43.     mngBttnInteraction.cubeMap.GetComponent
44.     <MeshRenderer> (). materials [4] .SetTexture ("_ MainTex",  
45.    (Texture2D) Instantiate (skybox.GetTexture ("_ LeftTex")));
46.    mngBttnInteraction.cubeMap.GetComponent
47.    <MeshRenderer> (). materials [5] .SetTexture ("_ MainTex",
48.    (Texture2D) Instantiate (skybox.GetTexture ("_ BackTex")));
49.      
50.    UpdateRotationCubemap (currentFrame.rotationOffset);
51.    mngBttnInteraction.ContainerNavigation.SetActive (true);
52. }

The problem is that by destroying the textures used it will destroy all its references and those that use it, leaving my cubemap without texture. To solve that, I need to intact (clone) the applied texture and then destroy it. But this leads to a notorious FREEZE of the system. Researching found that creating intangibles of objects or textures leads to a decrease in performance. For what I need if you can help me, perhaps to find a new way to do this effect, or to manage my ram memory when I download textures and destroy it.


Things you should know:
- Unity 2018.1.0.0f2
- Visual Studio 2017
- C#

Thank you very much
regards
Saludos!